There are two main competing thermal printing technologies used with media such as labels. Thermal ribbon transfer uses heat to transfer a wax based ink to a media producing relatively durable output. Direct thermal printers utilize a chemically coated paper that is marked by a chemical reaction in response to print head heat and that was widely used in previous generation facsimile machines and that has a relatively short output shelf life. Designers of thermal printing applications such as point of sale (POS) receipt applications and barcode printing applications typically consider the various advantages and disadvantages of each technology and select the appropriate technology for an application.
In the first technology, thermal ribbon transfer printers typically utilize a fixed width thermal print head. A rubber drive roller called a platen feeds a thermal transfer media stock passed the print head and a thin thermal transfer ribbon or foil is sandwiched between the print head and the media. The ribbon is typically a polyester film coated on the label side with a wax, wax-resin or pure resin ink. The ribbon is fed past the print head using a spooling mechanism having a source and uptake spool. Since the wax is designed to transfer at a single temperature, there has previously been no application for a multiple heat level thermal print head for use with thermal ribbon transfer printers. Multicolor thermal ribbon transfer printers are sometimes used for color label applications and have complicated media paths such as the CB-416-T3 Color Barcode Printer available from Toshiba TEC America of Atlanta, Ga. Similarly, a color thermal transfer printing process known as OPAL has been described by the Polaroid Corporation of Waltham, Mass.
In the second technology, direct thermal printers typically utilize a fixed width thermal print head. A rubber drive roller called a platen feeds a heat responsive direct thermal media stock passed the print head and the resistive heat elements are driven by the printer controller and element drivers to create the printed image. The media is typically a paper roll that is impregnated with a solid-state mixture of a dye and a suitable matrix. In a common POS receipt application, a monochromatic black media is utilized.
Certain dual color direct thermal printing systems have been developed that utilize relatively expensive dual color thermal media stock. For example, the TM-T88IV two-color direct thermal receipt printer is available from Epson America, Inc. of Long Beach, Calif. In such a system, the direct thermal media includes two different leuco dye reactions that occur at different temperatures. Accordingly, the printer will activate one temperature to print a fist color such as black and another temperature to print the second color such as blue. The colors available to such systems are limited by the availability of leuco dye chemistries for use in such media. Furthermore, the dual color direct thermal media may cost three times as much as a comparable roll of monochrome media. Conversely, thermal ribbon is available is virtually any color. There are also grayscale direct thermal systems available that are typically used in medical applications such as the Mitsubishi P-93W grayscale thermal printer Mitsubishi Digital Electronics America, Inc. of Irvine, Calif. Such systems utilize grayscale thermal media such as the Kanzaki KPT-1270 available from Kanzaki Specialty Papers of Springfield, Mass. that includes a leuco dye that is responsive to a range of heats to produce a range of gray scale intensities.
There are certain thermal printers that have been designed to alternatively operate in a direct thermal printing mode or a thermal ribbon transfer mode. For example, the CITIZEN CLP4081 thermal printer available from Citizen Systems Europe UK of Berkshire, United Kingdom can be configured to work in either a thermal transfer mode or a direct thermal transfer mode. It is of course possible that someone might have used direct thermal media stock in a thermal ribbon transfer printer instead of the typical thermal transfer stock. For example, the B700 thermal ribbon transfer postage meter available from Pitney Bowes Inc. of Stamford, Conn. utilizes a red thermal ribbon that transfers at about approximately in the range of 75 degrees Celsius. Such a printer might also mark a direct thermal media if it activates at the same temperature. However, the thermal transfer printer is a single heat monochromatic wax transfer technology. Even if the direct thermal media placed in that printer were to be activated at the temperature used by the thermal transfer printer, there would be no variance of the heat used to vary the color contribution of the direct thermal media.
Accordingly, there is a need for a multicolored thermal printer using relatively inexpensive thermal media. Additionally, there is a need to provide multicolored thermal printer using a single one-color thermal transfer ribbon.